System and method of assessing endothelial function

ABSTRACT

A medical diagnostic system and method for assessing endothelial function comprise adjusting a reactive hyperemia indicator, measured in response to a stimulus, based on an anthropomorphic and/or demographic variable. The adjusted reactive hyperemia indicator provides a more accurate reflection of endothelial function and can be communicated to a clinician.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage entry application of Internationalapplication no. PCT/US2016/040800, filed 1 Jul. 2016 and published on 5Jan. 2017 under International publication no. WO 2017/004571 (the '800application). This application claims priority to U.S. provisionalpatent application No. 62/187,793 titled “SYSTEM AND METHOD OF ASSESSINGENDOTHELIAL FUNCTION,” filed 1 Jul. 2015, which is hereby incorporatedby reference as though fully set forth herein. This application isrelated to U.S. application Ser. No. 12/483,930, filed 12 Jun. 2009 (the'980 application), now U.S. Pat. No. 8,057,400 B2, issued 15 Nov. 2011(the '400 patent). The '800 application; the '980 application; and the'400 patent are hereby incorporated by reference as though fully setforth herein.

FIELD

The present invention relates generally to assessing endothelialfunction in a mammal.

BACKGROUND

Cardiovascular disease is a leading cause of morbidity and mortality. Ithas been shown that the early stages of cardiovascular disease can bediagnosed by assessing the ability of the arteries to dilate in responseto an increase in blood flow. The degree of arterial dilation inresponse to an increased blood flow correlates with the severity ofcardiovascular disease.

Endothelial cells constitute the innermost lining of blood vessels andproduce nitric oxide, which is the predominant vasodilator in thearterial system. An increase in blood flow results in increased shearstress at the surface of endothelial cells and initiates a signalingpathway that results in phosphorylation and activation of nitric oxidesynthase, and increased production of nitric oxide. In addition toacting as a potent vasodilator, endothelium-derived nitric oxideinhibits many of the initiating steps in the pathogenesis ofatherosclerotic cardiovascular disease, including low-densitylipoprotein uptake, white cell adhesion to the vessel wall, vascularsmooth muscle proliferation, and platelet adhesion and aggregation.

Brachial artery flow-mediated dilation serves as a measure of thebioavailability of endothelium-derived nitric oxide in patients, and ithas been used extensively in large clinical studies to non-invasivelydetect systemic endothelial dysfunction.

Several invasive and non-invasive techniques have been developed toevaluate endothelial function. Invasive techniques, which involveintra-coronary or intra-brachial infusions of vasoactive agents, areconsidered to be the most accurate for the detection of endothelialdysfunction. Due to their highly invasive nature, the use of suchtechniques is limited and has led to the development of severalnon-invasive techniques. The ultrasound imaging of the brachial arteryis the most commonly employed non-invasive technique for the assessmentof the vasodilatory response. See, for example, Mary C. Corretti et al.J. Am. Coll. Cardiol. 2002; 39:257-265, which is incorporated herein byreference in its entirety. It utilizes continuous electrocardiogram(EKG) gated two-dimensional ultrasound imaging on the brachial arterybefore and after induction of arterial dilation by five-minute cuffocclusion of the arm. The ultrasound imaging technique is mostly used toassess (1) the changes in the diameter of the brachial artery induced byadministration of vasoactive drugs; and (2) flow-mediated dilation,which follows an occlusion of the brachial artery via inflating a cuffaround the limb. Once the cuff is released, the blood flow causes shearstress on the endothelium, which, in turn, produces vasoactivesubstances that induce arterial dilation. The increase in the diameterof the brachial artery in healthy people is higher than that in patientswith endothelial dysfunction. However, even in healthy people, themagnitude of the arterial dilation is not sufficient to be reliablydetermined by the ultrasound imaging technique. A trained andexperienced operator is essential in obtaining meaningful data with theultrasound imaging technique. This difficulty limits the testing ofarterial dilation with the ultrasound imaging technique to specializedvascular laboratories.

Most of the existing techniques do not quantify the amount of stimulusdelivered to the endothelium nor do they account for other sources ofnitric oxide such as the nitric oxide transported and released by theblood cells in response to hypoxemia induced by the temporary occlusionof the brachial artery. It has been shown that these factors cansignificantly affect the amount of flow-mediated dilation and,therefore, inject additional variability into the test results obtainedwith equipment that does not account for such factors.

U.S. Pat. No. 6,152,881 (to Rains et. al.), which is incorporated hereinby reference in its entirety, describes a method of assessingendothelial dysfunction by determining changes in arterial volume basedon measured blood pressure using a pressure cuff. The pressure cuff isheld near diastolic pressure for about ten minutes after an arteryocclusion until the artery returns to its normal state. The measuredpressure during this time is used to determine the endothelial functionof the patient. The extended period of applying cuff pressure to thelimb affects circulation, which in turn impacts the measurements.

U.S. Pat. No. 7,390,303 (to Dafni), which is incorporated herein byreference in its entirety, describes a method of assessing arterialdilation and endothelial function, in which the relative changes in thecross sectional area of a limb artery are assessed using a bio-impedancetechnique to monitor cross-sectional area of a conduit artery.Measurements of bio-impedance are difficult to perform. Sincebio-impedance measurements involve applying electrical to the skin ofthe patient, such measurements are poorly tolerated by patients due toskin irritation. Further, the measured signals vary greatly.

U.S. Pat. No. 7,074,193 (to Satoh et al.) and U.S. Pat. No. 7,291,113(to Satoh et al.), which are incorporated herein by reference in theirentirety, describe a method and apparatus for extracting components froma measured pulse wave of blood pressure using a fourth order derivativeand an n-th order derivative, respectively.

A clinical need exists for a system and method that are inexpensive,easy to perform, non-invasive, well tolerated by patients, and providean indication of the ability arteries to respond to an increase in bloodflow.

SUMMARY

Methods and diagnostic systems provide for assessing changes in arterialvolume of a limb segment of a mammal and for assessing endothelialfunction of a mammal. In one aspect, a diagnostic system determinesamplitudes of component pulse waves of detected volume pulse waves of alimb segment detected during a baseline period to determine a baselinearterial volume of the limb segment. The diagnostic system determinesamplitudes of component pulse waves of detected volume pulse waves ofthe limb segment detected during a time period after a stimulus has beenapplied to the mammal to induce a period of change in the arterialvolume of the limb segment. The diagnostic system determines relativechange in arterial volume of the limb segment during the time periodafter the stimulus relative to the arterial volume of the limb duringthe baseline period from the amplitudes of the component pulse waves ofthe detected volume pulse waves at baseline and after the stimulus.

In another aspect, the diagnostic system determines relative change inarterial volume by comparing the amplitudes of the component pulse wavesof volume pulse waves at baseline and after the stimulus.

In another aspect, the component pulse wave is an early systoliccomponent. In another aspect, the diagnostic system determines relativechange in arterial volume by comparing maximum amplitudes of the earlysystolic components of the volume pulse waves during the baseline periodand maximum amplitudes of the early systolic components of the volumepulse waves after the stimulus.

In another aspect, the diagnostic system monitors the limb segment todetect the detected volume pulse waves of the limb segment during thebaseline period, and monitors the limb segment to detect the detectedvolume pulse waves of the limb segment during an after-stimulus period.

In another aspect, a diagnostic system applies a stimulus to generatereactive hyperemia, measures a reactive hyperemia indicator, adjusts thereactive hyperemia indicator based on an anthropomorphic or demographicvariable to arrive at an endothelial function indicator, andcommunicates the endothelial function indicator to a clinician.

The features and advantages described in the specification are not allinclusive and, in particular, many additional features and advantageswill be apparent to one of ordinary skill in the art in view of thedrawings, specification, and claims. Moreover, it should be noted thatthe language used in the specification has been principally selected forreadability and instructional purposes, and may not have been selectedto delineate or circumscribe the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial diagram illustrating a diagnostic system inaccordance with the present invention.

FIG. 2 is a block diagram illustrating the diagnostic system of FIG. 1.

FIG. 3 is a flow chart illustrating an operation of arterial volumechange assessment of the diagnostic system of FIG. 1.

FIG. 4 is a timing diagram illustrating pressure applied to a limbduring baseline testing and analysis and after-stimulus testing andanalysis of FIG. 3 with an occlusion providing a stimulus.

FIG. 5 is a timing diagram illustrating amplitudes of early systoliccomponents of pulse waves measured during a baseline period and anafter-stimulus period of FIG. 4.

FIG. 6 is a graph illustrating correlation between the normalizedincreases in amplitudes of early systolic components of pulse waves of asegment of an arm as measured in some embodiments and the increases indiameter of the brachial artery measured via ultrasound imaging of thebrachial artery.

FIG. 7 is a timing diagram illustrating blood flow and systolic pressureafter release of the occlusion in FIG. 4.

FIGS. 8a and 8b are timing diagrams illustrating, in an expanded view,measured cuff pressure oscillations of a limb during oneinflation/deflation cycle of FIG. 4 before occlusion and during onecycle of FIG. 4, respectively, after occlusion of blood vessels in thelimb.

FIG. 9 is a timing diagram illustrating pressure applied to the limbduring the baseline testing and analysis and after-stimulus testing andanalysis of FIG. 3 with an oral administration of nitroglycerinproviding a stimulus.

FIG. 10 is a timing diagram illustrating amplitudes of early systoliccomponents of pulse waves measured during a baseline period, a stimulusperiod, and an after-stimulus period of FIG. 9.

FIG. 11 is a flow chart illustrating one embodiment of the operation ofarterial volume change assessment of FIG. 3.

FIG. 12 is a flow chart illustrating one embodiment of an operation ofdetermining amplitude of the arterial volume change assessments of FIGS.3 and 11.

FIG. 13 is a timing diagram illustrating a measured pulse wave for ahealthy person.

FIG. 14 is a timing diagram illustrating a measured pulse wave for apatient with cardiovascular disease.

FIG. 15 is a flow chart illustrating one embodiment of an operation ofdetermining changes in arterial volume of the operations of FIGS. 3 and11.

FIGS. 16A and 16B are flow charts illustrating embodiments of a processfor adjusting a reactive hyperemia indicator based on anthropomorphicand/or demographic variables.

DETAILED DESCRIPTION

A preferred embodiment of the present invention is now described withreference to the figures where like reference numbers indicate identicalor functionally similar elements. Also in the figures, the leftmostdigits of each reference number corresponds to the figure in which thereference number is first used.

FIG. 1 is a pictorial diagram illustrating a diagnostic system 100 (alsoreferred to herein as the ANGIODEFENDER system) in accordance with thepresent invention. The diagnostic system 100 comprises a diagnosticdevice 102, a diagnostic computer 104, a cuff 106, a Doppler transducer108, and an oxygen saturation (StO₂) sensor 110.

As used herein, the volume pulse waves are oscillations in the bloodpressure between the systolic and the diastolic pressures of arteries.The diagnostic system 100 detects the volume pulse waves and performsdiagnostics for assessing arterial volume changes of a limb segmentbased on the detected pulse waves. In some embodiments, the volume pulsewave includes a composite pulse wave formed of a superposition of aplurality of component pulse waves. The component pulse waves partiallyoverlap and the arterial pulse wave shape or contour is formed by thesuperposition of the component pulse waves. The component pulse wavesmay include, for example, an incident systolic wave (also called earlysystolic wave), a reflected wave (also called late systolic wave), andother waves. The diagnostic system 100 measures amplitudes of componentsof arterial volume pulse waves as a way of monitoring the changes inarterial volume of the limb segment after a stimulus. While it may beeasier to measure the amplitude of the whole arterial volume pulse wave,the timing of the component pulse waves shifts throughout the testingprocedure and changes the shape of the pulse wave. In some embodiments,the diagnostic system 100 measures amplitude of a physiologicallysignificant component (such as a component pulse wave) of the volumepulse wave to assess the changes in arterial volume of the limb segment.The diagnostic system 100 may use any component pulse wave of thedetected volume pulse wave or portion thereof (such as maximum,inflection point, or amplitude at a fixed time of the component pulsewave), any portion of the volume pulse wave (such as maximum, inflectionpoint, or amplitude at a fixed time of the volume pulse wave), or acombination thereof for the diagnostics for assessing arterial volumechanges. As an illustrative example, the operation of the diagnosticsystem 100 is described herein in terms of the early systolic wave.

In use, the cuff 106 is disposed around a limb 120 so that when the cuff106 is inflated, the cuff 106 constricts a segment of the limb 120. Itis understood by those skilled in the art that the measurements of thechanges in the arterial volume of a limb segment described herein arenot measuring the volume changes of only a single artery in the limb120, but are measuring the volume changes in substantially all arteriesin the segment of the limb 120 that is being constricted. Although thevolume changes measurements and the physiology thereof are described fora single artery, one skilled in the art will recognize that theinvention is not restricted to a single artery and that the volumechanges measurements are of all or substantially all arteries in thesegment of the limb being measured. The limb 120 may be any limb ordigits thereof, but for the sake of simplicity, the limb 120 isdescribed as an arm, and the artery that is being evaluated is describedas the brachial artery. In some embodiments, the limb 120 is a leg andthe artery is a femoral artery. Although the diagnostic system 100 isdescribed for use on a human being, the invention is not so limited. Thediagnostic system 100 can be used on other mammals.

The diagnostic computer 104 provides control signals to the diagnosticdevice 102 and receives information and detected data from thediagnostic device 102.

The diagnostic device 102 provides air to and releases air from the cuff106 via a tube 112 of the cuff 106. The diagnostic device 102 maycontrol, detect and monitor the air pressure in the tube 112. In someembodiments, a gas other than air, or a liquid, such as water, may beused in the cuff 106, the tube 112, and the pneumatic module 202 (seeFIG. 2). In some embodiments, the cuff can be an electrically-controlledelastomer or a mechanically-controlled material.

Although the diagnostic system 100 is described herein as applying apressure via the cuff 106 to the limb 120 to occlude an artery 122 as astimulus of the endothelium as blood flows into the artery 122 afterrelease of the occlusion, other forms of stimuli may be provided. Invarious embodiments, the stimulus of the endothelium comprises amechanical stimulation, a thermal stimulation, a chemical stimulation,an electrical stimulation, a neurological stimulation, a mentalstimulation or a stimulation via physical exercise, or any combinationthereof, to induce a change in arterial volume of the limb segment. Thestimuli are well known and some of them induce formation of nitric oxideby the endothelial cells lining the walls of the arteries. In someembodiments, the stimulus to the endothelium can also be delivered inany way that transiently and locally increases the blood flow and shearstress at the arterial wall. For instance, this can be achieved byapplying ultrasound waves such that it creates turbulence inside a majorartery. The chemical stimulation may be, for example, a vasoactiveagent, such as an oral administration of nitroglycerol, or anintra-brachial infusion of acetylcholine.

The diagnostic device 102 provides control signals to and receivesmeasurement signals from the Doppler transducer 108 and the oxygensaturation (StO₂) sensor 110. The Doppler transducer 108 and the oxygensaturation (StO₂) sensor 110 are used in some embodiments for thepurpose of quantifying the amount of a vasodilatory stimulus, such as atransient occlusion of the arteries of the limb segment.

The Doppler transducer 108 is disposed on the limb 120 and adjacent tothe artery 122 in the limb 120 and distal or proximal from the cuff 106for measuring blood flow velocity in the artery 122 using a Dopplerprocess. The Doppler transducer 108 may be any conventional Dopplertransducer designed to measure blood flow velocity in a conduit artery.In some embodiments, the diagnostic system 100 does not include aDoppler transducer 108.

The oxygen saturation (StO₂) sensor 110 is disposed on the limb 120 anddistal from the cuff 106 for measuring oxygen levels in the tissue ofthe limb to determine the extent to which hemoglobin in the tissue issaturated with oxygen. The oxygen saturation (StO₂) sensor 110 may beany conventional StO₂ sensor. In some embodiments, the diagnostic system100 does not include an oxygen saturation (StO₂) sensor 110.

Although the Doppler transducer 108 and the oxygen saturation sensor 110are described herein as an apparatus to quantify the amount of stimulusvia occlusion, other apparatus to quantify the amount of vasoactivestimuli may be provided.

Although the diagnostic computer 104 is described herein as performingthe control, computation, and analysis of the diagnostic system 100, theinvention is not so limited. The diagnostic device 102 may include aprocessor or microcontroller for performing any or all of the operationsdescribed herein as being performed by the diagnostic computer 104.

Although the diagnostic computer 104 is described herein as being localto the blood diagnostic device 102, the diagnostic computer 104 may becoupled to the diagnostic device 102 through a communication line,system, or network, such as the Internet, wireless, or landline. Forexample, the operation of the diagnostic device 102 may be done near thepatient while the diagnostic computer 104 may remotely process the data.

FIG. 2 is a block diagram illustrating the diagnostic device 102. Thediagnostic device 102 comprises a pneumatic module 202, a pressuredetector 204, a Doppler transducer system 206, an oxygen saturation(StO₂) sensor system 208, and an interface 210. The pneumatic module 202controls pressure in the cuff 106 in response to control signals fromthe diagnostic computer 104. The pneumatic module 202 comprises a pump222 (e.g., an air pump) for pressurizing air, a reservoir 224 forstoring the pressurized air, and a pressure controller 226 forcontrolling the release of air via the tube 112 into the cuff 106.

The pressure detector 204 comprises a pressure sensor electronics system228 for controlling a pressure sensor 230, which senses pressure in thecuff 106 via the tube 112. The pressure sensor 230 detects pressureoscillations in the cuff 106 resulting from pulse waves in the artery122. In some embodiments, the pressure sensor 230 is disposed in thecuff 106 or in the tube 112. In some embodiments, the pressure sensor230 is a plethysmography sensor, such as a reflectivephoto-plethysmography sensor.

The interface 210 communicates control signals and information signalsbetween the diagnostic computer 104 and the pneumatic module 202, thepressure detector 204, the Doppler transducer system 206, and the oxygensaturation (StO₂) sensor system 208. The interface 210 may include aprocessor or microcontroller for performing any or all of the operationsdescribed herein.

The Doppler transducer system 206 communicates with the Dopplertransducer 108 for measuring blood flow velocity in the artery 122. Insome embodiments, the diagnostic computer 104 commands the Dopplertransducer system 206 to measure blood flow velocity through the artery122 after the cuff pressure has been released to assess the amount ofstimulus delivered via shear stress to the artery 122.

In some embodiments, the diagnostic computer 104 may include test dataof blood velocity and may use such test data to quantify the amount ofthe post-occlusion stimulus in a patient. The diagnostic computer 104may use this data as part of the assessment of changes in the arterialvolume of the limb segment described herein.

The oxygen saturation (StO₂) sensor system 208 communicates with theoxygen saturation (StO₂) sensor 110 to measure oxygen levels in thetissue for determining the extent to which the hemoglobin in the bloodof the tissue is saturated with oxygen.

In some embodiments, the diagnostic computer 104 may include test dataof oxygen saturation and may use such test data to standardize thedegree of limb ischemia among the test subjects, and quantify the amountof the post-occlusion stimulus in a particular patient. The diagnosticcomputer 104 may use this data as part of the assessment of changes inthe arterial volume of the limb segment described herein.

FIG. 3 is a flow chart illustrating an operation of arterial volumechange assessment of the diagnostic system 100. Before operating thediagnostic system 100, the cuff 106 is placed around the limb 120 (e.g.,arm) of the patient. The test is started with an entry on the diagnosticcomputer 104 in any well known manner such as keystrokes on a keyboard(not shown) or movement of a cursor and selection of a screen button viaa mouse (not shown). In response to an initiation of the diagnosticcommand, the diagnostic computer 104 assesses changes in the arterialvolume of a segment of the limb 120. The diagnostic computer 104performs baseline testing and analysis (block 302) during a baselineperiod 402 (see FIG. 4 below). In some embodiments, the diagnosticsystem 100 detects and analyzes volume pulse waves of a segment of thelimb 120 during the baseline period in which no stimulus is applied tothe patient. In some embodiments, the analysis of the volume pulse wavesincludes determining amplitudes of the detected volume pulse waves tocalculate a baseline arterial volume of the segment of the limb 120. Oneembodiment of the baseline testing is described below in conjunctionwith FIG. 4.

A stimulus is applied to the patient to induce a period of change inarterial volume of the segment of the limb 120 (block 304) during astimulus period 404 (see FIG. 4 below). In some embodiments, thediagnostic computer 104 commands the pneumatic module 202 to pressurizethe cuff 106 to a level sufficient to occlude the artery 122. In someembodiments, the cuff 106 is inflated to a pressure above systolic for aperiod of time sufficient to induce change in arterial volume of thesegment of the limb 120 after releasing the cuff pressure.

The diagnostic computer 104 performs after-stimulus testing and analysis(block 306) during an after-stimulus period 406 (see FIG. 4 below). Insome embodiments, the diagnostic system 100 detects and analyzes volumepulse waves of a segment of the limb 120 after the stimulus, such as apredetermined time after either starting or terminating the applicationof the stimulus. In some embodiments, the analysis of the volume pulsewaves includes determining amplitudes of early systolic components ofthe detected volume pulse waves to calculate an after-stimulus arterialvolume of the segment of the limb 120. One embodiment of theafter-stimulus testing is described below in conjunction with FIG. 4.The analyses of blocks 302 and 306 may be performed separately from thetesting and at a later time.

The diagnostic computer 104 performs an arterial volume changeassessment (block 308). In some embodiments, the diagnostic computer 104calculates the relative change in arterial volume of the limb 120 duringthe after-stimulus time period 406 (see FIG. 4 relative to the arterialvolume of the limb 120 during the baseline period 402 (see FIG. 4) fromthe amplitudes of the early systolic component of volume pulse waves atbaseline and after the stimulus. One embodiment of the arterial volumechange assessment is described below in conjunction with FIG. 15.

In some embodiments, the assessment of the level of hypoxemia (or oxygensaturation) can be included in the arterial volume change assessment(block 308) and achieved by any method that is compatible with thetesting procedure (e.g., based on non-pulsatile measurements ofhypoxemia if a cuff 106 is used to occlude the artery). In someembodiments, the assessment of post-occlusion blood velocity or bloodshear stress can be included in the arterial volume change assessment(block 308) and achieved by any method that is compatible with thetesting procedure (e.g., based on Doppler measurements).

FIG. 4 is a timing diagram illustrating pressure applied to the limb 120during the baseline testing and analysis (block 302) and after-stimulustesting and analysis (block 306) of FIG. 3 with an occlusion providing astimulus. Prior to the procedure described in FIG. 4, a patient's bloodpressure is measured to select an individualized pressure that will beapplied to the limb. During blood pressure measurements, the diagnosticsystem 100 determines systolic, diastolic, and mean arterial pressures,which may be done in a conventional manner. Once the blood pressuremeasurements are performed, the individualized pressure applied to thepatient's limb is determined as a percentage of diastolic, or systolic,or mean arterial pressure. It can also be determined according to aformula based on the patient's blood pressure. For instance, thepressure applied to the patient's limb may be computed as the patient'sdiastolic pressure minus 10 mm Hg. Standardization of the pressureapplied to each patient allows the comparison of the test data amongpatients in whom blood pressures are different.

As an illustrative example, during a baseline period 402 (e.g., 150seconds), the diagnostic device 102 measures the resting arterial volumepulse waves of the brachial artery 122, which are indicative of theresting diameter of the brachial artery 122. During the baseline period402, the diagnostic system 100 commands the diagnostic device 102 toperform a series of rapid inflations 412 and deflations 414 of the cuff106, and to collect data from the pressure sensor 230. (For the sake ofclarity, only ten inflations 412 and ten deflations 414 are shown, butother numbers may be used. For the sake of clarity only oneinflation/deflation cycle is labeled.) In each cycle, the cuff israpidly inflated 412 to a pressure, such as the sub-diastolic arterialpressure, and held inflated 416 for a predetermined time (e.g., 4 to 6seconds) and then held deflated 418 for a predetermined time (e.g., 4 to10 seconds). In some embodiments, the diagnostic computer 104 maydynamically determine the time of the inflation 416 and the number ofpulses based on the measurements. While the cuff 106 is inflated 416,the diagnostic device 102 detects a plurality of pressure oscillations(or volume pulse waves).

After the baseline period 402, the diagnostic device 102 inflates thecuff 106 to a supra-systolic pressure (e.g., systolic pressure plus 50mm Hg) to temporarily occlude the artery 122 for an occlusion period 403(e.g., about 300 seconds). Concurrent with the occlusion, the oxygensaturation (StO₂) sensor electronics 208 controls the oxygen saturation(StO₂) sensor 110 to monitor the level of hypoxemia in the limb distalto the occluding cuff.

Thereafter, the diagnostic device 102 rapidly deflates the cuff 106(e.g., to a pressure below venous pressure, for instance, below 10 mmHg) to allow the blood flow to rush into the limb 120 during a stimulusperiod 404. The pressure release of the cuff 106 creates a rapidincrease in the blood flow in the artery 122, which generates shearstress on the endothelium of the brachial artery 122. The shear stressstimulates the endothelial cells to produce nitric oxide (NO), whichdilates the artery 122.

Concurrent with the cuff deflation, the Doppler transducer electronics206 controls the Doppler transducer 108 to collect data for apredetermined time (e.g., 10-180 seconds) during which time the Dopplertransducer 108 measures blood velocity.

During an after-stimulus period 406, the diagnostic system 100 commandsthe diagnostic device 102 to perform a series of rapid inflations 422and deflations 424 of the cuff 106, and to collect data from thepressure sensor 230 in a manner similar to that for the baseline period402 for a predetermined time (e.g., 1-10 minutes). (For the sake ofclarity, only fourteen inflations 422 and fourteen deflations 424 areshown, but other numbers may be used. For the sake of clarity only oneinflation/deflation cycle is labeled.) In each series, the cuff israpidly inflated to a pressure, and held inflated 426 for apredetermined time (e.g., 4 to 6 seconds), and then deflated 428. Insome embodiments, the diagnostic computer 104 may dynamically determinethe time of the inflation 426 and the number of pulses detected based onthe measurements. During this time, the diagnostic computer 104 monitorsthe dynamics of changes in arterial volume of a limb segment (a gradualincrease in pulse wave amplitude to maximum and then a gradual decreasein the pulse wave amplitude to return to a resting state).

FIG. 5 is a timing diagram illustrating amplitudes of early systoliccomponents of pulse waves measured during the baseline period 402 andthe after-stimulus period 406 of FIG. 4.

FIG. 6 is a graph illustrating correlation between the normalizedincreases in amplitudes of early systolic components of volume pulsewaves of a segment of an arm as measured in some embodiments and theincreases in diameter of a brachial artery measured via ultrasoundimaging of the brachial artery. Each data point in the graph correspondsto a different patient. The stimulus in both methods was a 5-minuteocclusion of the brachial artery via cuff inflation to a supra-systolicpressure. A normalization of the test results obtained with the presentinvention accounts for the fact the diagnostic system 100 assesses thechange in the volume of substantially all arteries in the limb segment,while the ultrasound imagining visualizes only the main artery.

FIG. 7 is a timing diagram illustrating blood flow and systolic pressureafter release of the occlusion in FIG. 4 during the stimulus period 404.A line 701 shows a rapid increase in blood flow followed by a decreaseto normal flow. A line 702 shows the temporary drop in systolic pressureafter the occlusion.

FIGS. 8a and 8b are timing diagrams illustrating measured cuff pressureoscillations of the limb 120 during one inflation/deflation cycle beforeocclusion (FIG. 8a ) and during one cycle after occlusion (FIG. 8b ) ofblood vessels in the limb 120 in an expanded view. During the cuffpressure sequence, data is collected about the oscillations in the cuffpressure due to the pulsation of the brachial artery. The changes in theoscillatory amplitude (or the amplitude of a pulse wave) are related tothe changes in the radius of the brachial artery, and FIG. 8b shows thepulse wave amplitude after occlusion being larger than the pulse waveamplitude before occlusion.

In some embodiments, arterial volume pulse waves are detected using anexternal pressure that is applied to the segment of the limb 120. Insome embodiments, the externally applied pressure varies graduallybetween near-systolic and near-diastolic. In some embodiments, theexternal pressure is applied by initially applying the external pressureat a pressure near systolic, and gradually reducing the externalpressure to a pressure near diastolic. In some embodiments, the externalpressure is applied by initially applying the external pressure at apressure near diastolic, gradually increasing to a pressure nearsystolic at a rate to allow the oscillations to be detected, and thenquickly decreasing the pressure.

In some embodiments, as shown in FIGS. 4 and 9, an applied externalpressure is cycled between a high level and a low level so that thearterial volume pulse waves are determined while the external pressureis at the high level. In some embodiments, the high level is belowdiastolic pressure and the low level is below venous pressure.

In some embodiments, the high level 416 or 426 is maintained for no morethan 10 seconds in any cycle. In some embodiments, the low level 418 or428 is maintained for at least 4 seconds in any cycle. In someembodiments, the measurements are taken over at least one cardiac cycle.

FIG. 9 is a timing diagram illustrating pressure applied to the limb 120during the baseline testing and analysis (block 302) and after-stimulustesting and analysis (block 306) of FIG. 3 with an oral administrationof nitroglycerin providing a stimulus. Because there is no occlusionperiod 403, the diagnostic system 100 generates a series of rapidinflations 422 and deflations 424 with an inflation state 426 andmeasures the volume pulse waves during the baseline period 402, thestimulus period 404 and the after-stimulus period 406.

FIG. 10 is a timing diagram illustrating amplitudes of early systoliccomponents of pulse waves measured during the baseline period 402, thestimulus period 404 and the after-stimulus period 406 of FIG. 9.

FIG. 11 is a flow chart illustrating one embodiment of the operation ofarterial volume change assessment (block 308 of FIG. 3). In response toan initiation of the diagnostic command from the user, the diagnosticcomputer 104 assesses change in the arterial volume of a segment of thelimb 120. The diagnostic device 102 detects volume pulse waves of asegment of the limb during the baseline period 402, such as describedabove in conjunction with FIGS. 4-8 (or FIGS. 9-10, depending on thestimulus) (block 1102). In some embodiments, the diagnostic computer 104commands the pneumatic module 202 to pressurize the cuff 106 to a levelsufficient for the pressure detector 204 to detect volume pulse waves ofa segment of the limb 120.

The diagnostic device 102 determines amplitudes of early systoliccomponents of the detected volume pulse waves (block 1104). In someembodiments, the diagnostic computer 104 commands the pressure detector204 to detect volume pulse waves of the segment of the limb 120. Thediagnostic computer 104 analyzes the waveforms of the detected volumepulse waves and determines relevant amplitudes of the volume pulse wavesfor the baseline period. In one embodiment, the relevant amplitude of apulse wave is the difference between the maximum and the minimumpressures of the pulse wave. In some embodiments, the relevant amplitudeis the amplitude of the early systolic component. One embodiment fordetermining amplitudes of block 1104 is described below in conjunctionwith FIG. 12. (Blocks 1102 and 1104 may be used for the block 302 ofFIG. 3).

The diagnostic device 102 applies a stimulus during the stimulus period402 to induce a period of change in arterial volume of the segment ofthe limb 120 (block 1106). In some embodiments, the diagnostic computer104 commands the pneumatic module 202 to pressurize the cuff 106 to alevel sufficient for occluding the artery 122. (Block 1106 may be usedfor the block 306 of FIG. 3; other examples of stimuli are describedabove in conjunction with FIG. 1 and FIGS. 9-10).

The diagnostic device 102 detects volume pulse waves of the segment ofthe limb 120 during the after-stimulus period 406 to detect change inarterial volume of a limb segment, such as described above inconjunction with FIGS. 4-8 (block 1108). In some embodiments, thediagnostic computer 104 commands the pneumatic module 202 to pressurizethe cuff 106 to a level sufficient for the pressure detector 204 todetect volume pulse waves of a segment of the limb 120.

The diagnostic device 102 determines amplitudes of early systoliccomponents of the detected volume pulse waves after the stimulus (block1110). In some embodiments, the diagnostic computer 104 commands thepressure detector 204 to detect volume pulse waves of the segment of thelimb 120. The diagnostic computer 104 analyzes the waveforms of thedetected volume pulse waves and determines relevant amplitudes of thevolume pulse waves for the baseline period. In one embodiment, therelevant amplitude of a pulse wave is the difference between the maximumand the minimum pressures of the pulse wave. In some embodiments, therelevant amplitude is the amplitude of the early systolic component. Oneembodiment for determining amplitudes of block 1110 is described belowin conjunction with FIG. 12. (Blocks 1108 and 1110 may be used for theblock 306 of FIG. 3).

The diagnostic device 102 performs an arterial volume change assessment(block 1112). In some embodiments, the diagnostic computer 104calculates the relative change in arterial volume of the limb segment120 during the after-stimulus time period 406 relative to the arterialvolume of the limb 120 during the baseline period 402 from theamplitudes of the early systolic component of volume pulse waves atbaseline and after the stimulus. In some embodiments, the diagnosticcomputer 104 calculates the relative change by comparing the amplitudesof early systolic component of volume pulse waves at baseline (block1104) and after the stimulus (block 1106). (Block 1112 may be used forthe block 308 of FIG. 3). One embodiment of the arterial volume changeassessment is described below in conjunction with FIG. 15.

FIG. 12 is a flow chart illustrating one embodiment of an operation ofdetermining amplitude of the arterial volume change assessments (block308 of FIG. 3 and block 1112 of FIG. 11). The diagnostic computer 104determines the amplitude of the early systolic component of a volumepulse wave by computing fourth derivative of the detected volume pulsewave (block 1202). The diagnostic computer 104 determines a time atwhich the fourth derivative crosses the zero-line for the third time(block 1204). (A third zero-line crossing 1322 of FIG. 13 below and athird zero-line crossing 1422 of FIG. 14 below.) In some embodiments,the diagnostic computer 104 may instead determine the second derivativeof the detected volume pulse wave. In some embodiments, the diagnosticcomputer 104 may instead determine an inflection point in the volumepulse wave and use the time of occurrence of the inflection point. Insome embodiments, the diagnostic computer 104 may instead use Fouriertransformation of the volume pulse wave to determine the time ofoccurrence of the peaks of the pulse component pulse waves.

The diagnostic computer 104 determines a pressure value on the detectedvolume pulse wave at that time (block 1206). The diagnostic computer 104determines a pressure value at the beginning of the volume pulse wave(block 1208). In some embodiments, the diagnostic computer 104determines the pressure value at the beginning of the volume pulse waveby determining a minimum during the diastolic component of the pulsewave. The diagnostic computer 104 assesses the amplitude of the earlysystolic component of the volume pulse wave as the difference betweenthe pressure values (block 1210).

In some embodiments, the diagnostic computer 104 may compute otherorders of derivatives in block 1202, or not compute a derivative, butinstead determine the inflection point corresponding to the peak of theearly systolic component of the pulse wave by other methods. In otherembodiments, the diagnostic computer 104 may determine the maximumamplitude of the arterial volume pulse waves.

FIG. 13 is a timing diagram illustrating a measured pulse wave for ahealthy person. A pulse wave 1300 includes an early systolic component1302 and a late systolic component 1304. (The pulse wave 1300 mayinclude other component pulse waves, which are not shown.) The earlysystolic component 1302 forms an inflection point 1310 in the pulse wave1300. Because of the amplitude and the timing of the late systoliccomponent 1304, the maximum of the pulse wave 1300 coincides with thepeak of the early systolic component 1310. A line 1320 is a fourthderivative of the pulse wave 1300 and includes a third zero-linecrossing point 1322. The crossing point 1322 is used to determine thetime and amplitude 1312 of the early systolic component.

During the after-stimulus period, the shape of the arterial volume pulsewave changes to a pulse wave 1350. The pulse wave 1350 includes an earlysystolic component 1352 and a late systolic component 1354. (The pulsewave 1350 may include other component pulse waves, which are not shown.)The early systolic component 1352 forms an inflection point 1360 in thepulse wave 1350. During the after stimulus period, the amplitude and thetiming of the late systolic component 1352 change slightly and themaximum 1366 of the pulse wave 1350 no longer coincides with the peak ofthe early systolic component 1360. Yet, the amplitude 1362 of the earlysystolic component 1352 and the amplitude (distance 1362 plus thedistance 1364) of the maximum 1366 of the pulse wave 1350 differslightly.

FIG. 14 is a timing diagram illustrating a measured pulse wave for apatient with cardiovascular disease. A pulse wave 1400 includes an earlysystolic component 1402 and a late systolic component 1404. (The pulsewave 1400 may include other component pulse waves, which are not shown.)The early systolic component 1402 forms an inflection point 1410 in thepulse wave 1400. Because of the amplitude and the timing of the latesystolic component 1404, the maximum of the pulse wave 1400 coincideswith the peak of the early systolic component 1410. A line 1420 is afourth derivative of the pulse wave 1400 and includes a third zero-linecrossing point 1422. The crossing point 1422 is used to determine thetime and amplitude 1412 of the early systolic component.

During the after-stimulus period, the shape of the arterial volume pulsewave changes to a pulse wave 1450. A pulse wave 1450 includes an earlysystolic component 1452 and a late systolic component 1454. (The pulsewave 1450 may include other component pulse waves, which are not shown.)The early systolic component 1452 forms an inflection point 1460 in thepulse wave 1450. During the after stimulus period the amplitude and thetiming of the late systolic component change significantly and themaximum 1466 of the pulse wave 1450 no longer coincides with the peak ofthe early systolic component 1460. The amplitude 1462 of the earlysystolic component 1452 and the amplitude (distance 1462 plus thedistance 1464) of the maximum 1466 of the pulse wave 1450 differsignificantly.

The diagnostic system 100 may use the differences in the pulse wavecharacteristics of FIGS. 13-14 to compute arterial indexes (forinstance, the augmentation index) to assess the cardiovascular status ofthe patient.

FIG. 15 is a flow chart illustrating one embodiment of an operation ofdetermining changes in arterial volume of the operations of FIGS. 3 and11. The diagnostic computer 104 determines average pulse wave amplitudeper each inflation/deflation cycle over the measurement period andobtains a graph such as the graph described above in conjunction withFIG. 5.

The diagnostic computer 104 calculates an average (AVG_(baseline)) ofthe calculated average amplitudes of the early systolic components ofpulse wave measured during the baseline 402 (block 1502). For theafter-stimulus period 406, the diagnostic computer 104 calculates acurve that fits the after-stimulus data of the early systolic componentsof pulse wave measured during the after-stimulus 406 (block 1504), usingfor example, a fourth-order polynomial function. The diagnostic computer104 calculates a maximum (MAX_(after)) of the fitted curve of theafter-stimulus data (block 1506). The diagnostic computer 104 calculatesa time from the end of the occlusion (or other stimulus) to the maximumof the fitted curve of the after-stimulus data (block 1508). Thediagnostic computer 104 calculates a relative amplitude change from thebaseline to the maximum of the fitted curve of the after-stimulus data(block 1510).

The diagnostic computer 104 calculates relative change in arterialvolume ΔV (block 1512) as follows:ΔV=[(MAX_(after)−AVG_(baseline))/AVG_(baseline)]

The diagnostic computer 104 calculates relative change in arterialradius as follows (block 1512):ΔR=[(ΔV+1)^(1/2)−1],The relative change in radius ΔR is defined as follows:ΔR=[(R _(after) −R _(baseline))/R _(baseline)],where R_(after) is the maximum after-stimulus radius of the artery andR_(baseline) is the arterial radius at baseline.

In some embodiments, the diagnostic computer 104 may compute an areaunder the fitted curve for the after-stimulus data, in addition to orinstead of the determination of the maximum of the fitted curve of block1506. In some embodiments, the diagnostic computer 104 determines thearea under the curve by integrating the fitted polynomial function ofblock 1504 from the time the stimulus ends to either the time when themeasured amplitude returns to the baseline or to the end of the test. Insome embodiments, the diagnostic computer 104 extrapolates the fittedcurve of block 1504 to the time at which the measured amplitude returnsto baseline. In some embodiments, the diagnostic computer 104 computesother parameters (e.g., the width at half-height) from the fitted curveof block 1504 to calculate the relative change in arterial volume.

The diagnostic computer 104 may provide any or all of the raw data andprocessed data to a doctor or clinical researcher via a display, paperor other manners well known to those skilled in the art. In someembodiments, the diagnostic computer 104 provides a doctor processeddata such as 1) relative % change in arterial volume of a limb segmentafter a stimulus (for example, after 5 min cuff occlusion, the arterialvolume changed by 57%) as a reflection of the ability of the arteries todilate in response to the stimulus; 2) computed relative maximum %change in the radius of the artery after the stimulus; time to maximumchange in arterial volume (for instance, 72 sec); 4) area under thecurve; and 5) pulse wave characteristics (time difference between thepeaks of early and late systolic waves, augmentation index, etc.) asindicators of arterial stiffness. In some embodiments, the diagnosticcomputer 104 provides a doctor raw data, such as detected volume pulsewaves in each inflation/deflation cycles.

Although the diagnostic system 100 is described as including one cuff106, other numbers of cuffs 106 may be used. In some embodiments, thediagnostic system 100 includes two cuffs 106. One cuff 106 is disposedon the limb 120 and occludes the artery 122, and the other cuff 106 isdisposed on the limb 120 distal to the first cuff 106, and detects thepressure oscillations. Alternatively, one cuff 106 is disposed on thelimb 120 and detects the pressure in the artery 122, and the other cuff106 is disposed on the limb 120 distal to the first cuff 106, andoccludes the artery 122.

In an embodiment, the diagnostic computer 104 can provide a percentageof flow-mediated dilation (% FMD), that has been used as an indicator ofendothelial function. The % FMD can be determined by the diagnosticcomputer 104 based on the change in arterial volume post-occlusion vs.pre-occlusion, which, in turn, can be determined from the percent changein blood pressure post-occlusion vs. pre-occlusion, as measured by cuff106 and reflected as pulse wave amplitude changes by pressure sensor 230(described above with respect to FIGS. 1 and 2). This unadjusted % FMDdetermined by diagnostic computer 104 will henceforth be referred to as“AD-% FMD_(U)” to indicate that it is derived from the ANGIODEFENDERsystem described above and in the '400 patent. While AD-% FMD_(U) iscomparable to % FMD determined using brachial artery ultrasound imaging(BAUI-% FMD), the gold standard for measuring flow-mediated dilation,the correlation between AD-% FMD_(U) and BAUI-% FMD¹ can be furtheroptimized. Therefore, the present inventors have developed an algorithm,based on anthropomorphic demographic factors, for adjusting AD-% FMD_(U)to better correlate with BAUI-% FMD. ¹It should be noted that BAUI-%FMD, as used herein, includes both unadjusted BAUI-% FMD measurementsand BAUI-% FMD measurements that have been adjusted based on baselinebrachial artery size or other allometric factors. Unadjusted BALI-% FMDis calculated based on the percent change in brachial artery diameterpost-occlusion vs. pre-occlusion.

Based on data obtained using the ANGIODEFENDER system in a 29-personclinical pilot study conducted at Yale University in June through Augustof 2014, the present inventors initially determined that segregation ofsubjects by lean body mass (LBM), followed by subsequent adjustments tothe subjects' AD-% FMD_(U) based on mean arterial pressure (MAP) andpulse pressure (PP) or systolic blood pressure divided by diastolicblood pressure (SBP/DBP), yielded “adjusted AD-% FMD” (hereinafter AD-%FMD_(A)) values that were more comparable (based on Deming regressionanalysis) to BAUI-% FMD. It was further determined that both stepsperformed in the given order—LBM segregation first followed bysubsequent adjustment of MAP, PP, or SBP/DBP—were necessary to achieveAD-% FMD_(A) values that correlate well with BAUI-% FMD and, therefore,provide an improved endothelial function indicator.

FIGS. 16A and 16B illustrates the initial adjustment processes 1600A and1600B the inventors applied to AD-% FMD_(U) values to obtain AD-%FMD_(A) values that more closely approximate BAUI-% FMD. At blocks 1602A(in FIG. 16A) and 1602B (in FIG. 16B), AD-% FMD_(U) values weredetermined using the ANGIODEFENDER technology. Specifically, at block1602A, AD-% FMD_(U) values were determined according to the followingequation:

$\mspace{20mu}{{{AD}\text{-}{FMD}_{U}} = \lbrack {{\lbrack {\lbrack {\frac{{PWA}_{{MA}\; X} - {PWA}_{PREOCC}}{{PWA}_{PREOCC}} + 1} \rbrack^{1/2} - 1} \rbrack*\lbrack {100/C} \rbrack{PWA}_{{MA}\; X}\text{:}\mspace{14mu}{Maximum}\mspace{14mu}{post}\text{-}{occlusion}\mspace{14mu}{pulse}\mspace{14mu}{wave}\mspace{14mu}{amplitude}\mspace{14mu}({PWA})\mspace{20mu}{PWA}_{PREOCC}\text{:}\mspace{14mu}{Median}\mspace{14mu}{pre}\text{-}{occlusion}\mspace{14mu}{PWA}\mspace{20mu} C} = 3.4} }$At block 1602B, AD-% FMD_(U) values were determined according to thefollowing equation:AD-FMD_(U)={[(FMD₁+1){circumflex over ( )}0.5]−1}*100/C, whereFMD₁={[PWA_(max)/(PWA_(preocc)){circumflex over ( )}d]−1}/PWA_(preocc)C=3.4d=1PWA_(max)=Maximum post-occlusion pulse wave amplitude (PWA)PWA_(preocc)=Median pre-occlusion PWA

At step 1604, the AD-% FMD_(U) values were segregated based on LBM. LBMwas determined according to the following equation:LBM(Lean Body Mass; kg)=((100−% BF)/100)*BMI*BSA% BF(% body fat)=((( Wt /(( Ht/100){circumflex over( )}2))*1.2)+(Age*0.23)−(Gender*10.8)−5.4)

-   -   Wt=weight (kg)    -   Ht=height (cm)    -   Age=years    -   Gender=male (1); female (0)        BMI(Body Mass Index)= Wt /(( Ht/100){circumflex over ( )}2))        BSA(Body Surface Area)=0.007184*(Ht{circumflex over        ( )}0.725)*(Wt{circumflex over ( )}0.425)        It should be noted, however, that alternate equations or methods        can be used to calculate LBM, as well as BMI and BSA. It is        believed that segregation based on LBM is important as a first        adjustment step because the cardiovascular system has evolved        for efficient distribution of metabolic substrates, such as        oxygen, to tissue mass with high metabolic potential (e.g. LBM).        LBM may be more reflective of metabolic potential than other        body size variables, such as weight. It should also be noted        that in some embodiments anthropomorphic and/or demographic        factors other than LBM can be used to segregate the AD-% FMD_(U)        values. Examples of such factors include height, weight, age,        gender, BMI, or BSA.

In the initial adjustment processes 1600A and 1600B, 35 kilograms (kg)was used as the threshold value by which to segregate LBM measurements.Thus, at block 1606A, subjects with LBM of 35 kg or greater wereseparated, and at block 1606B, subjects with LBM of less than 35 kg wereseparated.

At block 1608A, the AD-% FMD_(U) of subjects with LBM greater than orequal to 35 kg was divided by MAP² to arrive at the AD-% FMD_(A). Atblock 1608B (in FIG. 16A), the AD-% FMD_(U) of subjects with LBM lessthan 35 kg was divided by PP² to arrive at the AD-% FMD_(A).Alternatively, at block 1608C (in FIG. 16B), the AD-% FMD_(U) ofsubjects with LBM less than 35 kg was divided by (SBP/DBP)² to arrive atthe AD-% FMD_(A). MAP, PP, SBP, and DBP can all be determined by thediagnostic system 100 during baseline testing, prior to occlusion.

In an embodiment, the steps and equations of process 1600A can all becombined into a single equation in which LBM segregation is taken intoaccount. In one embodiment, the equation is as follows:AD-% FMD_(A)=[Int+{(10⁷*AD-% FMD_(U))/(Xpp*([j*PP]{circumflex over( )}z)+(1−Xmap)*([k*MAP]{circumflex over ( )}w))}]/slope

-   -   where:    -   Int=y-intercept of a least-squares regression line of {(10⁷*AD-%        FMD_(U))/(Xpp*([j*PP]{circumflex over        ( )}z)+(1−Xmap)*([k*MAP]{circumflex over ( )}w))} vs BAUI-% FMD    -   Xpp=ae{circumflex over ( )}[−be{circumflex over        ( )}(−c*(D_(PP)−LBM))]    -   Xmap=ae{circumflex over ( )}[−be{circumflex over        ( )}(−c*(D_(MAP)−LBM))]    -   slope=slope of a least-squares regression line of {(10⁷*AD−%        FMD_(U))/(Xpp*([j*PP]{circumflex over        ( )}z)+(1−Xmap)*([k*MAP]{circumflex over ( )}w))} vs BAUI-% FMD    -   Constants: j, z, k, w, a, b, c, Dpp, Dmap        -   [constant]{circumflex over ( )}[value]=‘constant’ raised to            the power designated by the ‘value’, in base 10        -   [constant]e{circumflex over ( )}[value]=‘constant’ raised to            the power designated by the ‘value’, in base e            In an example, the constant j is equal to about 4.4, the            constant k is equal to about 0.5, the constant z is equal to            about 3.2, the constant w is equal to about 4.5, the            constant a is equal to about 1, the constant b is equal to            about 2, and the constant c is equal to about 0.8. In an            example, Dpp is equal to about 31.9, Dmap is equal to about            33.4, slope is equal to about 0.7 and Int is equal to about            2.6.

Likewise, in another embodiment, the steps and equations of process1600B can all be combined into a single equation in which LBMsegregation is taken into account:AD-% FMD_(A)=[Int+{(10⁷*AD-% FMD_(U))/(X_((SBP/DBP))*([j*(SBP/DBP)]{circumflex over( )}z)+(1−Xmap)*([k*MAP]{circumflex over ( )}w))}]/slope

-   -   where:    -   Int=y-intercept of a least-squares regression line of {(10⁷*AD-%        FMD_(U))/(X_((SBP/DBP))*([j*(SBP/DBP)]{circumflex over        ( )}z)+(1−Xmap)*([k*MAP]{circumflex over ( )}w))} vs BAUI-% FMD    -   X_((SBP/DBP))=ae{circumflex over ( )}[−be{circumflex over        ( )}(−c*(D_((SBP/DBP))−LBM))]    -   Xmap=ae{circumflex over ( )}[−be{circumflex over        ( )}(−c*(D_(MAP)−LBM))]    -   slope=slope of a least-squares regression line of {(10⁷*AD-%        FMD_(U))/(X_((SBP/DBP))*([j*(SBP/DBP)]{circumflex over        ( )}z)+(1−Xmap)*([k*MAP]{circumflex over ( )}w))} vs BAUI-% FMD    -   Constants: j, z, k, w, a, b, c, D_((SBP/DBP)), Dmap        -   [constant]{circumflex over ( )}[value]=‘constant’ raised to            the power designated by the ‘value’, in base 10        -   [constant]e{circumflex over ( )}[value]=‘constant’ raised to            the power designated by the ‘value’, in base e            In an example, the constant j is equal to about 62.1, the            constant k is equal to about 0.5, the constant z is equal to            about 4, the constant w is equal to about 5, the constant a            is equal to about 1, the constant b is equal to about 2.8,            and the constant c is equal to about 2.4. In an example, Dpp            is equal to about 36, Dmap is equal to about 34.5, slope is            equal to about 0.725 and Int is equal to about −1.75.

In the above equations, MAP and PP or (SBP/DBP) are weighteddifferentially based on LBM. The greater the LBM, the more heavily MAPis weighted in the equation. Conversely, the smaller the LBM, the moreheavily the PP or (SBP/DBP) are weighted in the equation.

In an embodiment, AD-% FMD_(A) can be calculated by a processor (notshown) located within diagnostic computer 104. In an alternativeembodiment, raw data (e.g., LBM, MAP, PP, SBP, DBP, AD-% FMD_(U), andBAUI-% FMD) from the diagnostic computer 104 can be communicated, viawired or wireless means, to an external processor (not shown) configuredto calculate AD-% FMD_(A). The diagnostic computer 104 can further beconfigured to communicate the AD-% FMD_(A) to a clinician (e.g., adoctor, a nurse, a healthcare worker, or a clinical researcher).

While the above equation for AD-% FMD_(A) requires AD-% FMD_(U) as aninput value, other measures of reactive hyperemia can be used in placeof AD-% FMD_(U). For example, other hemodynamic parameters can be usedto measure reactive hyperemia after a stimulus has been applied to asubject. Some examples of such hemodynamic parameters include a bloodvolume; a blood pressure; an amplitude, frequency, or shape of aplethysmographic wave; a blood vessel diameter; peripheral arterial tonechanges; or any derivative thereof. These hemodynamic parameters thatserve as indicators of reactive hyperemia can be adjusted, similar toAD-% FMD_(U).

In addition, temperature can be used as a measure of reactive hyperemia.A change in the temperature of a digit (e.g., a fingertip) post-stimulusvs. pre-stimulus is an indication of reactive hyperemia and cantherefore be adjusted according the above equation, similar to AD-%FMD_(U). A change in fingertip temperature can be detected by atemperature sensor (not shown) communicatively linked to the diagnosticdevice 102 and/or the diagnostic computer 104.

Reference in the specification to “some embodiments” means that aparticular feature, structure, or characteristic described in connectionwith the embodiments is included in at least one embodiment of theinvention. The appearances of the phrase “in some embodiments” invarious places in the specification are not necessarily all referring tothe same embodiment.

Some portions of the detailed description that follows are presented interms of algorithms and symbolic representations of operations on databits within a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of steps (instructions)leading to a desired result. The steps are those requiring physicalmanipulations of physical quantities. Usually, though not necessarily,these quantities take the form of electrical, magnetic or opticalsignals capable of being stored, transferred, combined, compared andotherwise manipulated. It is convenient at times, principally forreasons of common usage, to refer to these signals as bits, values,elements, symbols, characters, terms, numbers, or the like. Furthermore,it is also convenient at times, to refer to certain arrangements ofsteps requiring physical manipulations of physical quantities as modulesor code devices, without loss of generality.

However, all of these and similar terms are to be associated with theappropriate physical quantities and are merely convenient labels appliedto these quantities. Unless specifically stated otherwise as apparentfrom the following discussion, it is appreciated that throughout thedescription, discussions utilizing terms such as “processing” or“computing” or “calculating” or “determining” or “displaying” or“determining” or the like, refer to the action and processes of acomputer system, or similar electronic computing device, thatmanipulates and transforms data represented as physical (electronic)quantities within the computer system memories or registers or othersuch information storage, transmission or display devices.

Certain aspects of the present invention include process steps andinstructions described herein in the form of an algorithm. It should benoted that the process steps and instructions of the present inventioncould be embodied in software, firmware or hardware, and when embodiedin software, could be downloaded to reside on and be operated fromdifferent platforms used by a variety of operating systems.

The present invention also relates to an apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may comprise a general-purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program may be stored in a computerreadable storage medium, such as, but is not limited to, any type ofdisk including floppy disks, optical disks, CD-ROMs, magnetic-opticaldisks, read-only memories (ROMs), random access memories (RAMs), EPROMs,EEPROMs, magnetic or optical cards, application specific integratedcircuits (ASICs), or any type of media suitable for storing electronicinstructions, and each coupled to a computer system bus. Furthermore,the computers referred to in the specification may include a singleprocessor or may be architectures employing multiple processor designsfor increased computing capability.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems may also be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will appear from the description below.In addition, the present invention is not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof the present invention as described herein, and any references belowto specific languages are provided for disclosure of enablement and bestmode of the present invention.

Any numerical values or ranges presented herein include a range of +100%to −50% when proceeded by terms like “about” or “approximately.”

While particular embodiments and applications of the present inventionhave been illustrated and described herein, it is to be understood thatthe invention is not limited to the precise construction and componentsdisclosed herein and that various modifications, changes, and variationsmay be made in the arrangement, operation, and details of the methodsand apparatuses of the present invention without departing from thespirit and scope of the invention as it is defined in the appendedclaims.

What is claimed is:
 1. A method for assessing endothelial function in amammal, the method comprising: applying, using a cuff, a stimulus togenerate reactive hyperemia in a limb of the mammal; measuring, usingone or more processor, a reactive hyperemia indicator based on at leastone physiological parameter detected by one or more sensors; adjusting,using the one or more processors, the reactive hyperemia indicator basedon an anthropomorphic and/or demographic variable to determine anendothelial function indicator; and displaying, using a display, theendothelial function indicator to a clinician.
 2. The method of claim 1,wherein the anthropomorphic or demographic variable comprises a leanbody mass of the mammal.
 3. The method of claim 1, wherein the reactivehyperemia indicator comprises at least one of a hemodynamic parameter ora temperature.
 4. The method of claim 3, wherein the hemodynamicparameter comprises at least one of a volume; a pressure; an amplitude,a frequency, or a shape of a plethysmographic wave form; a blood vesseldiameter; peripheral arterial tone changes; or any derivative thereof.5. The method of claim 3, wherein the temperature comprises a fingertiptemperature.
 6. The method of claim 1, wherein the reactive hyperemiaindicator comprises a percentage of flow-mediated dilation.
 7. Themethod of claim 6, wherein measuring the percentage of flow-mediateddilation comprises assessing a change in arterial volume of a limbsegment of the mammal.
 8. The method of claim 7, wherein assessing thechange in arterial volume of the limb segment comprises: determiningamplitudes of component pulse waves of detected volume pulse waves ofthe limb segment detected during a baseline period prior to applying thestimulus to determine a baseline arterial volume; determining amplitudesof component pulse waves of detected volume pulse waves of the limbsegment detected during a time period after the stimulus has beenapplied to determine a post-stimulus arterial volume; and determiningrelative change in arterial volume of the limb segment based on thedifference between the baseline arterial volume and the post-stimulusarterial volume.
 9. The method of claim 8, wherein the component pulsewave is an early systolic component.
 10. The method of claim 6, whereinadjusting the reactive hyperemia indicator comprises approximating ameasure of reactive hyperemia based on brachial artery ultrasoundimaging.
 11. The method of claim 1, wherein the adjusting step furthercomprises using an algorithm to adjust the reactive hyperemia indicatorbased upon (i) a lean body mass of the mammal and (ii) at least one of apulse pressure, a systolic blood pressure, a diastolic blood pressure,and a mean arterial pressure of the mammal.
 12. The method of claim 11,wherein the pulse pressure, the systolic blood pressure, the diastolicblood pressure, and the mean arterial pressure are determined prior tomeasuring the reactive hyperemia indicator.
 13. The method of claim 11,wherein the adjusting step further comprises using the algorithm toadjust the reactive hyperemia indicator based upon the pulse pressureand the mean arterial pressure, and wherein the pulse pressure and themean arterial pressure are differentially weighted in the algorithm. 14.The method of claim 13, wherein the greater the lean body mass, the morethe mean arterial pressure is weighted in the algorithm.
 15. The methodof claim 13, wherein the smaller the lean body mass, the more the pulsepressure is weighted in the algorithm.
 16. The method of claim 13,wherein the algorithm comprises:$\mspace{20mu}{{{AD}\text{-}{FMD}_{U}} = \lbrack {{\lbrack {\lbrack {\frac{{PWA}_{{MA}\; X} - {PWA}_{PREOCC}}{{PWA}_{PREOCC}} + 1} \rbrack^{1/2} - 1} \rbrack*\lbrack {100/C} \rbrack{PWA}_{{MA}\; X}\text{:}\mspace{14mu}{Maximum}\mspace{14mu}{post}\text{-}{occlusion}\mspace{14mu}{pulse}\mspace{14mu}{wave}\mspace{14mu}{amplitude}\mspace{14mu}({PWA})\mspace{20mu}{PWA}_{PREOCC}\text{:}\mspace{14mu}{Median}\mspace{14mu}{pre}\text{-}{occlusion}\mspace{14mu}{PWA}\mspace{20mu} C} = 3.4} }$wherein AD-FMD_(U) comprises an unadjusted percentage of flow-mediateddilation as determined by ANGIODEFENDER technology.
 17. The method ofclaim 11, wherein the adjusting step further comprises using thealgorithm to adjust the reactive hyperemia indicator based upon theratio of systolic blood pressure to diastolic blood pressure and themean arterial pressure, and wherein the ratio of systolic blood pressureto diastolic blood pressure and the mean arterial pressure aredifferentially weighted in the algorithm.
 18. The method of claim 17,wherein the greater the lean body mass, the more the mean arterialpressure is weighted in the algorithm.
 19. The method of claim 17,wherein the smaller the lean body mass, the more the ratio of systolicblood pressure to diastolic blood pressure is weighted in the algorithm.20. The method of claim 17, wherein the algorithm comprises:AD-FMD_(U)={[(FMD₁+1){circumflex over ( )}0.5]−1}*100/C; whereinFMD₁={[PWA_(max)/(PWA_(preocc)){circumflex over ( )}d]−1}/PWA_(preocc),C=3.4, d=1, PWA_(max)=Maximum post-occlusion pulse wave amplitude (PWA),PWA_(preocc)=Median pre-occlusion PWA, and AD-FMD_(U) comprises anunadjusted percentage of flow-mediated dilation as determined byANGIODEFENDER technology.
 21. The method of claim 1, wherein the appliedstimulus comprises at least one of a mechanical stimulation, a thermalstimulation, a chemical stimulation, an electrical stimulation, aneurological stimulation, a mental stimulation, or a physical exercisestimulation.
 22. The method of claim 1, wherein the applied stimuluscomprises an inflated cuff disposed on a limb segment of the mammal, theinflated cuff imparting a supra-systolic pressure for a time periodsufficient to induce reactive hyperemia upon release of thesupra-systolic pressure.
 23. A system for assessing endothelial functionin a mammal, the system comprising: a means for applying a stimulus togenerate reactive hyperemia in a limb of the mammal; a means formeasuring a reactive hyperemia indicator based on at least onephysiological parameter detected by one or more sensors; a means foradjusting the reactive hyperemia indicator based on an anthropomorphicor demographic variable to determine an endothelial function indicator;and a means for displaying the endothelial function indicator to aclinician.
 24. The system of claim 23, wherein the anthropomorphic ordemographic variable comprises a lean body mass of the mammal.
 25. Thesystem of claim 23, wherein the reactive hyperemia indicator comprisesat least one of a hemodynamic parameter or a temperature.
 26. The systemof claim 25, wherein the hemodynamic parameter comprises at least one ofa volume; a pressure; an amplitude, a frequency, or a shape of aplethysmographic wave form; a blood vessel diameter; peripheral arterialtone changes; or any derivative thereof.
 27. The system of claim 25,wherein the temperature comprises a fingertip temperature.
 28. Thesystem of claim 23, wherein the reactive hyperemia indicator comprises apercentage of flow-mediated dilation.
 29. The system of claim 28,wherein a means for measuring the reactive hyperemia indicator comprisesa means for assessing a change in arterial volume of a limb segment ofthe mammal.
 30. The system of claim 29, wherein a means for assessingthe change in arterial volume of the limb segment comprises: a means fordetermining amplitudes of component pulse waves of detected volume pulsewaves of the limb segment detected during a baseline period prior toapplying the stimulus to determine a baseline arterial volume; a meansfor determining amplitudes of component pulse waves of detected volumepulse waves of the limb segment detected during a time period after thestimulus has been applied to determine a post-stimulus arterial volume;and a means for determining relative change in arterial volume of thelimb segment based on the difference between the baseline arterialvolume and the post-stimulus arterial volume.
 31. The system of claim30, wherein the component pulse wave is an early systolic component. 32.The system of claim 28, wherein a means for adjusting the reactivehyperemia indicator comprises a means for approximating a measure ofreactive hyperemia based on brachial artery ultrasound imaging.
 33. Thesystem of claim 23, wherein the means for adjusting further comprises ameans for using an algorithm to adjust the reactive hyperemia indicatorbased upon (i) a lean body mass of the mammal and (ii) at least one of apulse pressure, a systolic blood pressure, a diastolic blood pressure,and a mean arterial pressure of the mammal.
 34. The system of claim 33,wherein the pulse pressure, the systolic blood pressure, the diastolicblood pressure, and the mean arterial pressure are determined prior tomeasuring the reactive hyperemia indicator.
 35. The system of claim 33,wherein the means for adjusting further comprises a means for using thealgorithm to adjust the reactive hyperemia indicator based upon thepulse pressure and the mean arterial pressure, and wherein the pulsepressure and the mean arterial pressure are differentially weighted inthe algorithm.
 36. The system of claim 35, wherein the greater the leanbody mass, the more the mean arterial pressure is weighted in thealgorithm.
 37. The system of claim 35, wherein the smaller the lean bodymass, the more the pulse pressure is weighted in the algorithm.
 38. Thesystem of claim 35, wherein the algorithm comprises:$\mspace{20mu}{{{AD}\text{-}{FMD}_{U}} = \lbrack {{\lbrack {\lbrack {\frac{{PWA}_{{MA}\; X} - {PWA}_{PREOCC}}{{PWA}_{PREOCC}} + 1} \rbrack^{1/2} - 1} \rbrack*\lbrack {100/C} \rbrack{PWA}_{{MA}\; X}\text{:}\mspace{14mu}{Maximum}\mspace{14mu}{post}\text{-}{occlusion}\mspace{14mu}{pulse}\mspace{14mu}{wave}\mspace{14mu}{amplitude}\mspace{14mu}({PWA})\mspace{20mu}{PWA}_{PREOCC}\text{:}\mspace{14mu}{Median}\mspace{14mu}{pre}\text{-}{occlusion}\mspace{14mu}{PWA}\mspace{20mu} C} = 3.4} }$wherein AD-FMD_(U) comprises an unadjusted percentage of flow-mediateddilation as determined by ANGIODEFENDER technology.
 39. The system ofclaim 33, wherein the means for adjusting further comprises a means forusing the algorithm to adjust the reactive hyperemia indicator basedupon the ratio of systolic blood pressure to diastolic blood pressureand the mean arterial pressure, and wherein the ratio of systolic bloodpressure to diastolic blood pressure and the mean arterial pressure aredifferentially weighted in the algorithm.
 40. The system of claim 39,wherein the greater the lean body mass, the more the mean arterialpressure is weighted in the algorithm.
 41. The system of claim 39,wherein the smaller the lean body mass, the more the ratio of systolicblood pressure to diastolic blood pressure is weighted in the algorithm.42. The system of claim 39, wherein the algorithm comprises:AD-FMD_(U)={[(FMD₁+1){circumflex over ( )}0.5]−1}*100/C; whereinFMD₁={[PWA_(max)/(PWA_(preocc)){circumflex over ( )}d]−1}/PWA_(preocc),C=3.4, d=1, PWA_(max)=Maximum post-occlusion pulse wave amplitude (PWA),PWA_(preocc)=Median pre-occlusion PWA, and AD-FMD_(U) comprises anunadjusted percentage of flow-mediated dilation as determined byANGIODEFENDER technology.
 43. The system of claim 23, wherein theapplied stimulus comprises at least one of a mechanical stimulation, athermal stimulation, a chemical stimulation, an electrical stimulation,a neurological stimulation, a mental stimulation, or a physical exercisestimulation.
 44. The system of claim 23, wherein the applied stimuluscomprises an inflated cuff disposed on a limb segment of the mammal, theinflated cuff imparting a supra-systolic pressure for a time periodsufficient to induce reactive hyperemia upon release of thesupra-systolic pressure.
 45. A non-transitory machine-readable mediumencoded with instructions, that when executed by one or more processors,cause the processor to carry out a process for assessing endothelialfunction in a mammal, the process comprising: controlling a cuffconfigured to apply a stimulus to generate reactive hyperemia in a limbof the mammal; measuring a reactive hyperemia indicator based on atleast one physiological parameter detected by one or more sensors;adjusting the reactive hyperemia indicator based on an anthropomorphicor demographic variable to determine an endothelial function indicator;and controlling a display to display the endothelial function indicatorto a clinician.